My rb had tiagra rd. Worked fine for me for almost 4 years. Only changed it to 105 coz had a crash that destroyed the rd, and got good price on 105. I'm using Sora shifters but I haven't noticed any difference.

My CX has Tiagra shifters and rd. I have a very slight preference for tiagra shifters but no deal-breaker for either one.

Would like a 10 speed cassette not to make me faster, but to have closer gear ratios. Again, no deal breaker. In fact I rather like the stronger chain of 8/9 speed over 10.