Quote: "I have made several medium size, terrainy outdoor environments
and the BEST fps I've EVER got (even when all scenes were custom made to be low poly) is around 25. mostly slinking back to around 20, and as low as 10"
Looks like all you really need is more ram.
The comp I test on has lower specs than yours, with a gig of ram.
fpsc v1.4
1024mb ram
1.80 ghz processor
Nvidea GO 6100 512mb integrated.
Personally I cant comment on the maps you have built or the media you have used, but I can assure you that large outdoor environments need not lag badly if optimised fully.
I see a lot of posts saying this and that cant be done mostly with outdoor maps, such as enemy collision wont work properly with custom terrain, which can be achieved, not easily, but it can be done.
The reason I say all this is that I know with some work it is entirely possible, you say what you know from your own tests and I also, my own experience says it can be done
Image from Eldora, fps31 constant (no mod) FPSC V 1.4.
This level had a lot of terrain, trees cottage, walls etc, lower levels had a lot of tunnels, theres a lot of media in there not just what you see in the image, no lag, had one point next to a tree where the player could be stuck due to overhang from leaves, solved by making the leaves no collision. The thing most likely to make this level lag was the sunbeam decals.