wes, i have the very kit you are considering... 4x5 arca swiss f-line metric with 8x10 format kit. i started with 4x5 and just very recently added the 8x10 back. the f-line cameras are, imho, the finest cameras on the planet. the 8x10 format kit is simply brilliant, and takes about 5 seconds to make the switch. the bellows are FANTASTIC, allowing you to use lenses from 75mm (if there was one that covered the format) to 600mm. after going through many cameras, this is the system i have finally ended up with and feel there's simply nothing out there that comes close to it. do yourself a favor, start with the arca and never look back! if i were doing it all over again, i'd still start with 4x5 and add 8x10 later, just be sure in building your lens kit that they will cover both formats. knowing that the jump was in my future, i built my kit with 8x10 coverage in mind...

75 Nikkor SW (only 4x5)
110 Super Symmar XL
150 Super Symmar XL
210 APO Sironar-S
305 G-Claron
355 Schneider Gold Dot Dagor
450 Fuji-C
600 Fuji-C

good luck!
scott