2Mbps is in no way "too high": it's the standard maximum speed served by SL sim servers to each connected viewer for UDP messaging
(this bandwidth setting does not affect HTTP messaging, in either the Cool VL Viewer or any other viewer). It's also just a default: if you want to see things getting sluggish, nothing prevents you to reduce that UDP bandwidth setting. Note however, that in today's viewers and grids, most things now happen via HTTP messaging at an even higher and unlimited (or rather only limited by your connection performances) bandwidth.
It's 500 MB (mega bytes) and 1000 MB (1 Gb), not 500 KB and 1000 KB !!!
This cache size setting is almost only about the textures. In my 9+ years SLing experience, a large cache doesn't speed up things that much: if you roam a lot of different sims, hardly coming back to most of them in the next few days, the cache will never be large enough to hold all the textures of the sims you visited, and when/if you come back to one of the sims, the textures will have been wiped out anyway. If you don't roam dozens of sims, then a 1Gb large cache is large enough to retain the textures of the sims you visit every day.
I will increase the limit for next releases, but most people won't see a difference... You are the one and only person to request a cache size increase so far...
If your router "crashes" with such a load as a SL viewer, then I don't even want to think about what it would do when faced with, say, torrent downloads, HD TV streaming, and other bandwidth/connections hungry applications. Note that the Cool VL Viewer (v1.26.17 branch, with LL's viewer-azumarill LLCore HTTP code backport) is the only TPV so far to provide you with the best connection efficiency (less ports open, better bandwidth per port via less latency per HTTP request and pipelining).
In any case, if your so-called "router" chokes or crashes, trash it and buy a *proper* router (which can open up to the 65535 possible ports simultaneously on each IP address it serves): it's not a viewer (or torrent downloader, etc) issue, but a bad/poor network device issue on your end !
If you knew me better, you'd know that the size of the "user base" (and I assume you mean Cool VL Viewer user base, here) is not my concern at all... I made the Cool VL Viewer for myself and I'm only sharing it for like-minded people to enjoy it: if you don't like how it works, please feel free to use another viewer...