if you put in the 20 to 30 hrs aweek like I do, you'll be fine
i find I have problems when I am forced to use certain control mechanisms.
I NEVER user turn keys by choice only when I am forced to - only use forwards / backwards and strafe - with mouse look to steer ... I find it give a far more smooth, far more natural feel.
When I change from one game to another, I tend to spend quite awhile tweaking sensitivities. I have been a hard core CS'r for quite some time. When I switched between 1.5 / 1.6 ... CZ and Source, I always speed a couple of days re tweaking , usually due to me having updated the mouse drivers or turned something on/off.
Either way, one or two clicks on the sensitivty either way can mean the difference between feeling connected or detached from whats going on in the screen.
I find the more closely you get the turn / mouse speed to what is natural for you to be able to balance your ability to move around along with also being able to getting your cursor accurately and quickly over the target.
I think finding that balance is often the key:
a) its the optimum point for you to be effective
b) it 'feels' the most fluid and offers the least stress to your hand / eye co-ordination.
I see players with really high sense settings ( mouse sensitivity ) and some seem to be able to play that way .... but alot are sacrificing the ability to precisely focus against the abilty to get somewhere quick..... me, I can't tell whats going on at that speed.
Probably why I play CS on Friendly fire servers - kids that jump around and shoot everything that blurs past them need to stick to quake or get auto banned for team killing on our servers
I've never had motion sickenss from playing by preparing the interface the instant I am not happy with it....... but I might be just not prone to motion sickness either.