Hi Kartik,
Thanks for the wishes !
To my understanding and experience, none of the Prep tests available can predict your actual score very accurately. On the real test, there are upto 8 or 9 questions in each section that do not contribute to your actual score, this scoring pattern is not recreated in any prep test (including GMATPrep). Also the scoring algorithm of many prep tests may not have the latest percentile inputs. For eg. I remember seeing a forum member with a 750 with the exact same Q-V breakdown as me. Basically the percentiles on the real test keep getting updated while the prep tests, including the GMATPrep tests are not updated as frequently. So I'd warrant a guess and say that the performance for which you get a particular score is being constantly altered by GMAC.
I also have a strong feeling that the first 15 questions determine the specific range within which you will finally score. I would also rate the actual test to be slightly harder than GMATPrep tests, I got some very interesting questions with false logic answers which I was only able to do because of experience. I was able to confidently predict my Quant score between 50-51 because I had reached a point where I could see patterns & repeated answering logics and was consistently getting the same score everywhere. The same, however, was not true for my Verbal score, it was erratic, and jumped all over the place on different tests. Though in real life I would say they are both equally strong.
Anyways, according to all the expert comments I have seen, your real GMAT score can go +/- 30 from your real talent. So, for eg. I might have gottena 750 or a 760 if I had gotten maybe an experimental question wrong instead of a counted one. Luck also plays a factor

I would note that the veritas tests I took were at my home, and no matter how close to test conditions I tried to get, there is a definite comfort factor when you are in familiar surroundings, this is absent on the real thing. And, as you mentioned, test day pressure also plays a role.
Everything being said, I would rate Veritas Prep tests very highly and I went over each test multiple times during review. THe Quant is approx. GMAT level, if very slightly lacking in 700+ level questions (I saw some very easy Q questions on veritas prep towards the end many times ! ). The Verbal is the real gem with a number of great questions, it does have its faults though, some of the passages and CR questions are NOTHING like the real thing, SC shines through. I have a feeling that the scoring algorithm is also not that updated since a V51 is highly unlikely to appear ever. Use it for the material

So, it is somewhat harder that GMATPrep but I'd highly recommend doing them both.
Congrats for the score and wish you luck for your apps. From what you have mentioned here I agree with most of them except this "On the real test, there are upto 8 or 9 questions in each section that do not contribute to your actual score, this scoring pattern is not recreated in any prep test (including GMATPrep)" . I think that's a pretty big number for number of anchor questions. To the best of my knowledge it is 4/section and they don't really contribute to your score.