I went from 105 on my first bike (now parked on the trainer) to Force on my second bike. I had no problems with Shimano but now prefer Sram. I'd characterize Shimano as having a mushier feel, while Sram shifts into gear more with a cleaner and more emphatic feel. In my experience the double-tap system is easy to get used to, even switching between bikes (and thus brands) with some regularity. I like having shifting independent of the brake levers. The shape of the hoods is different between the brands and that for me was more of an adjustment than the shifting. If you make the switch, you may find you like gloves with different padding than you've used with Shimano. Enjoy your test ride!

Just read your reply and have to add I just don't find Sram difficult to shift. I would say my 105 is more difficult shifting to the big chain ring.