Resolution Audio Opus 21 or GNSC moddedd 50/55

After much cogitating and a recent chance audition of the RA Opus 21, I decided it is the player for me. However, I am well aware of the excellent work done by GNSC on modding the players. So the question, would I be better off with a stock Opus 21, or a reference modded RA 50 or 55? As a 2nd question, would the 50 or 55 be better. If they can be found second hand, the 2 options are about the same price.
Before anyone suggests it, I can't really go for the Opus 21 and mod it later. I live in the UK and the costs of sending a unit to the US and back+ local import taxes, would be prohibitive. I plan to buy in the US and have it modded before sending to England.
Has anyone had a chance of comparing the 2 options, or can comment on the benefits of a reference upgrade, I would be grateful?

Happy to discuss this directly with you if you can contact me off line. Not sure how many people out there have made these direct comparrisons which we of course have...I'm happy to guide you to a good decision for your needs.

I have both the Opus and the CD55 right now. I love 'em both. For the money the CD55 is a really strong performer.

Having said that, I am keeping Opus. Its is only slightly better in my system. The Opus is a little dryer sounding and has slightly better resolution.

The CD55 has fuller Bass and a slightly richer tone in the lower midrange.

So IMO, with my warmish speakers and Bass heavy room, the Opus was a winner but only by a nose.

Both of these are two of the best CDPs I have come in contact with. As far as the Mods... Steve at GNSC is the man .
A little late to your party and you've made a decision I'm sure, but I am so delighted with my GNSC Opus 21, I thought I'd chime in....

I have not heard the modified 55 or the stock 55 for that matter, but I have now used/owned a stock Opus, as well as the GNSC Opus. I must say, the modified Opus is head and shoulders superior to the stock Opus. If you can swing the modified Opus do yourself, as well as anyone else in the home, a favor and get it! If you can't afford it, I will speculate the modified CD55 will better the stock Opus. The GNSC mods are that good. Hope you've contacted Steve, he's a good guy to deal with....