Going for a very low mount set up is very over rated imho - makes the longer shots harder, it's a better benefit to have a slightly higher set up and keep the rail.
I use low mounts (for scopes upto 32mm obj), which gives me a scope to barrel centre of 1.82" - which is the same as an s400 on high mounts.
With these mounts, the objective bell end sits below the rail.
see here: http://elmerfud0-0.piczo.com/?g=55046164&cr=5
The biggest negative point of ditching the rail is risk of damaging the dovetails on the block, which you really don't want to be doing