If you are after extracting maximum performance from a pistol, the conventional wisdom is the avoid using gases that contain a silicone lubricant mixed in. Theory being that the lubricant gets blown by the action onto the hop rubber, reducing the hop effect or providing inconsistency. The downside is that the various orings and seals in the magazines and gun itself like some silicone on them to keep them sealing nicely. This explains the Honourable Puceflange's post above where he mentioned the use of UltraAir (a silicone free airsoft gas) with the occasional use of a 'green' gas with added silicon to lubricate the seals.
If your pistol is reserved only for close up engagements, then you aren’t going to notice much of a difference if you were to use a silicon containing gas however - so your choice whether the extra (potential) maintenance hassle is worth it. Personally I run without any silicon mixed into my gas, but that's more me just being tight (I use a plumbers bottles of pure Propane in conjunction with an adapter). I add a few drops of silicone every now and then to the pistols blow back unit, and whenever one of the mags starts leaking (pretty rare to be honest) and tightening the baseplate or valves doesn't do the trick; depending where the leak is, I either remove the base plate and use silicone grease around its big oring/gasket before re-sealing, or work some silicone oil into the internals of the valves. It's all dead easy, and dead quick to do - like 5 mins max...