i used to use road pedals on my giant and my raleigh and tbh at my level of cycliing i notice no difference whatsoever between spd's and spd-sl pedals - both clip my feet to the bike and both feel equally as comfortableI suspect that once you try road pedals you won't feel the need to ask those questions anymore.
thats just my honest and not so experienced opinion as i've only been cycling two years