Question for "terrain gurus".

From those who are familiar with terrain mechanism in FS, I'd like to ask for some input.My single performance issue with FS is a drop in FPS coupled with stutterings when FS9 loads (a lot of) texture files from /scenery/world/textures. Other than that, my FPS is locked at 25 and stays there most of the time and is smooth. The drop happens every few minutes if I fly a high and fast jet. It's almost not a problem for me if I fly low and slow. My config is: AMD 64 3200+ | 1 GB ram | 7800GT I use FS-GS tweak, I use FSAUTOSTART, I defragment my drive everyday, AA at 2 and AF at 4, I use my computer for FS only.I don't use addon airports but what I do use is FSglobal2005 mesh, Holger's great free mesh sceneries in Seatle area & flight evironment textures. I use ASv6, my sight distance in FS is 60 miles and 59 miles in ASv6. Cloud draw distance is 40 miles and coverage is max. Cloud layers is limited to 3 using ASv6.Now I think the performance problem is directly related to my terrain settings. In FS I check "extended terrain texture", "terrain detail" slider is on "none", In FS9.cfg I have TERRAIN_DEFAULT_RADIOUS=9 & TERRAIN_EXTENED_RADIOUS=4, TEXTURE_BANDWIDTH=280. I like seeing texture on distant terrains and I like ground textures to be sharp and focused around the plane. But I am wondering that my such preferrence and settings is making FS load too much detailed textures on each draw and drags down the whole game. Could some terrain gurus give me some ideas on whether my "loading too much textures" theory make sense? Could someone tell me what the TERRAIN_DEFAULT_RADIOUS=9 & TERRAIN_EXTENED_RADIOUS=4 do and how are they different? What's the unit for the "9" & "4"? 9 miles? 90 miles?I appreciate it.Jason