Anyone use SMC wireless routers?

It will have roughly the same range as the other wireless equipment you've used. Disregard the specs unless your operating within a line of sight environment. If not then Mfg numbers are irrelevant. At the price point of SMC, Linksys, Dlink etc... you can flip a coin generally speaking. One model may outperform another (even within the same company, in fact two units of the same model may have different performance output. Nature of budget wireless gear) but by and large they are very similar overall.

CCNA, MCSE, A+, Cisco Certified Wireless Field Engineer

No way to be certain. Real world testing is the only way you'll know for sure. Stone can be a problem though, I'll say that, but you should be ok. You might not/probably won't associate at 54 Mb, so transferring files may be a dissapointment but you should have enough available bandwidth to stream those MP3's. Videos may be another story. I'd be cautiously optimistic but prepared for poor results in terms of video streaming. There is certainly a chance you won't get a link at all. 70 feet could be an issue with a stone wall in the path. Depends on the wall I suppose and other environment variable exlcusive to your location. Microwave is susceptible to alot of things that can cause interference. Any neighbors with wireless gear? That could be a problem outdoors. 2.4 Ghz phones and a myriad of other problems. Good luck.

CCNA, MCSE, A+, Cisco Certified Wireless Field Engineer