i cant say that i have used or have experience with the tanaka m700, but i have seen and used the M24 upgraded to the max.
considering they use basicly the same platform. the m24 was decent enough out of the box, but the one i knew belonged to my pal who runs one of main's 2 airsoft field and had more than enough money into it. lol, anyways that thing could hit a man size target from about 400 feet away maybe more. was a HPA rig and well with all the upgrades cost about $2,500 so it would be a pricey project for that level lol.
all in all i would say the M700 would be a good buy, plenty of upgrade potential in the future, really a nice gun that you can put as much as you want into it.