I think Tim Higgins compared Tomato to DD-WRT connection handling (or it was Tomshardware). Tim is the editor and reviewer for this site. I'm sure he'd have some input on this. If I remember correctly TOmato would get bogged down when flooded with connections and DD-WRT did much better, but things may have changed. When I briefly used Tomato and DD-WRT as my gateway, I did not encounter any slowdown or crashing under heavy load (QoS was enabled), but I am the only person on my LAN that uses P2P apps, so my experience may be different in a different household.
http://www.smallnetbuilder.com/lanwan/lanwan-features/30437-can-dd-wrt-or-tomato-fix-bad-routing
Most SOHO routers do not have an SSH server included natively in their firmware. You would need to find a router with third party DD-WRT/Tomato/OpenWRT etc firmware support.
If you do not wish to spend that much money on a 11n DD-WRT compatible router there are cheaper Netgear routers that support DD-WRT. If you buy them refurbished they are dirt cheap.
2.4Ghz 11n - Netgear WNR834B (all hardware revisions support DD-WRT) - $25
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3641947&CatId=2668
Selectable Dual Band 11n - Netgear WNDR3300 (5Ghz mode has very poor range because of cheap radio) - $40
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=4165406&CatId=2668
Both have 4MB flash for DD-WRT VPN builds and have 16MB of RAM which should be enough to handle many connections, but the CPU may likely struggle with many 1024-bit encrypted P2P packets but should work. The hardware is probably not much faster than the 200Mhz BCM CPU in the WRT54G. If you despise DD-WRT QoS, there is a DD-WRT QoS script generator for Windows floating around that works very well - it takes getting used to but is great if you don't frequently tinker with QoS settings.
Even the 300Mhz CPU on the WRT610N will cause traffic to slow if you have a fast upload link on your home broadband connection, the 610N has 64MB of RAM - plenty of room for large iptables cache. 610n 1.0 works but 610 v2.0 is a work in progress and the router is not fully functional after a DD-WRT flash.
You can also check craigslist for a cheap EOL Linksys WRT3XX or WRT150/160 v1.0.
The Linksys WRT160NL should in theory support DD-WRT without a VxWorks formatting step, but so far it only supports OpenWRT and you have to compile it from source yourself.
There are not many other11n router that have full DD-WRT support.
For the PC option, you can buy a (low power) HP t5700 thin client. It has relatively low power consumption (about 12W but can go as high a 20W). If you leave it on 24/7, it consumes about 0.36kWhr per day, which is about $0.02 (2 cents) per day and under ten dollars of electricity per year. You have to buy them on eBay and prices are about $70 for Buy-it-Now but can be cheaper with and auction and justsnipe.
http://shop.ebay.com/i.html?_nkw=hp+t5700&_sacat=0&_trksid=p3286.m270.l1313&_odkw=t5700&_osacat=0
The t5700 has a 733-1Ghz x86 emulated CPU which can run Windows XP or greater. It uses one laptop DDR1 memory module and usually comes with 256MB of system RAM (512MB max). For storage it has a 192-256MB flash drive with a laptop 44-pin IDE header, which I have replaced with a 60GB 2.5" IDE HDD (and a 40GB on the other). It has 4 onboard USB 1.1 (sorry no USB 2.0) ports and onboard sound and a VGA adapter as well as 100Mbit ethernet (on a jperf bandwidth test when it was running Windows XP, it was CPU limited at 60Mbit, which is fair).
the 1Ghz CPU is equivalent to a 400Mhz Pentium 3 when benchmarked using Sysoft Sandra. That is respectable all things considered and is more than adequate for high encryption SSH tunneling.
It also has the option of a regular PCI (33Mhz) card. It has the PCI slot on the motherboard, but the standard case is too small to house the PCI card, so you need to buy a $20 expansion bay case which includes a PCI riser card. With this you can install a second ethernet NIC to use it as a gateway running IPCOP/PFSense or whatever or put in USB 2.0 PCI card (but you won't be able to boot from devices connected to the expansion USB card).
I was able to buy two of them for $45 each (without HDD and RAM upgrades) and it was well worth it. One is a uTorrent mule, eDonkey mule, HFS server, SMB server (with USB 2.0 storage), Adito SSL VPN and FreeSSHd server running Windows XP - the other is just a WAMP server.
If you bought one for cheap, you would not need to upgrade a thing if you install Puppy Linux onto the Flash because it is only 100MB. You could then tunnel SSH through it. I don't know if you have enough space on the remaining flash to install Apache Tomcat and LAMP to get SSL VPN up and running, but you can find a cheap used 2.5" IDE HDD for it and install whatever OS. I don't know if it would boot from a SATA-IDE adapter bridge HDD, but you can try. If SSH is blocked at your remote location, you can always tunnel the SSH traffic through the SSL VPN tunnel (which is sometimes necessary because HTTPS port 443 is *almost* never blocked).
If you buy the PCI kit and a 100Mbit PCI ethernet NIC, you can turn it into a gateway (that has SSH) and should handle everything you throw at it including the encrypted P2P connections (looking at ~$100). Using the t5700 as a gateway is a little ambitious and may not appeal to some - so you can always use it for encoding and decoding and tunneling P2P traffic as a LAN client and have your current router passthorugh the SSH traffic. I would personally not buy the WRT610N because many of them are defective and probably won't offer much better performance than the WRT54GL the way you are using it. At least get the Netgear $25 router because it is a great deal and can double as a wireless bridge/Repeater if you decide not to use it.
You could always do your WOL solution with your existing rig.
