The Titan V is a datacenter/scientist-oriented card, while RTX20xx are the consumer-level cards. You will have to fully read the documentation of each to identify what they have in common, what is a full instruction/feature set in Titan V and what is a subset in RTX, and what is not present in RTX at all.
Rule of thumb is that you can expect stuff to perform faster on Titan V than on 2080Ti (which doesn’t mean the 2080 is slow by any means). One notable example is the memory bus of the 2080Ti, 352-bit, versus the 3072-bit on the Titan, which is ridiculously large. I have access to Titan V at work, and coding on a 1080Ti at home, I can tell you the thing is serious. I wish I had a Titan V at home but can’t justify the cost. Some guys here invested on a RTX and can provide better feedback on them.
Regarding large datasets, 2080Ti has 11GB while Titan V has 12GB, so you have similar room and if more memory is needed, then you have to look at the Teslas or multi-GPU setups.
The moderators and some very experienced contributors will provide much deeper feedback on recommendation.