Gas sniper's are not usually semi auto. The KJW 10/22 is not a "sniper", and the only other examples are the WE Dragunov and modified M14's.
I own a Tanaka L96, and personally think it is much better than spring bolt actions. The deciding factor for me was the bolt pull, because with a spring rifle you have the entire spring weight behind the bolt pull as opposed to the gas version which allows for smooth sliding action. Ammo capacity is usually around the same (14-26 rounds per mag) depending on your brand. IIRC the KJW M700 has a short mag with a 12 round capacity.
If this is your first gas gun I would recommend that you watch some videos or read up on basic gas gun maintenance, as they do take more upkeep than their springer counterparts. After each use I clean my bolt, mag, hopup and barrel and make sure everything is lubed properly. This ensures everything moves properly and keeps dirt from building up.
Also, there's the question of consistent performance. A well tuned spring rifle can put shots out within +/- 2 fps error, while gas guns are going to shoot at varied speeds on different days. Temperature and gas pressure come into play and this can be a deal breaker for people looking for very precise shots, well, as precise as they can get in airsoft. Then again, a well maintained gas gun with a regulated valve can shoot with within those same tolerances.
In the end it really boils down to personal preference. I like having a "weightless" bolt, and the longer barrel. The FPS never really varies enough to make a difference in accuracy IMO, but it's noticeable at the chrono station.
