It's a first class ticket so you can travel in first class. What you get in terms of service depends on the TOC.
Virgin and TPE were happy to provide a full service, including food and wine on Virgin. XC refused anything apart from a cup of coffee.
Interesting, I was told at Kings Cross that I could either take EMT to Derby or Sheffield or I could take Virgin to Manchester. I chose Virgin to Manchester as the EMT was only a five-coach Meridian and it looked rather snug on board.
The last time I had to travel to York during EC disruption I took the EMT/XC option. The 5-car 222 was completely rammed, and this didn't help me travelling with an oversized suitcase, as after seeing numerous passengers (rightly) told off for obstructing the ticket gates to try and see which train they should get on, I followed the advice of waiting to see which train it was. People slowly filtered through the gates anyway. After 10 minutes of waiting with no announcement I decided to wander out and find the train and sure enough, it had been boarding for those 10 minutes, and was already full. 7 passengers and 3 suitcases to a non-toilet-end vestibule (i.e. a handful of square meters at best) for the entire 2 1/2 hours to Sheffield was distinctly unpleasant.
The CrossCountry 220 from Sheffield was busy leading me to stand, but not excessively so, I had plenty of room there. The return journey was fine (I timidly bought separate return tickets to guarantee validity as on that occasion no announcement was made at KGX about them being valid by the time I abandoned the station), but the crowding on the outbound made me rethink how I'd do it next time.
This weekend then (Friday afternoon) I took the Virgin/TPE route. The 390 to Manchester was busy, but there were some seats at the front of the train, which the train manager kindly pointed out to people over the announcement, but walking through 4 carriages with my case was never going to work so I stood alone in the vestibule.
The TPE end of the journey was an absolute farce though. A 3-car train on a major route at peak commuter time seems a bit iffy to me anyway, but with the extra load, it was 100% full as far as Huddersfield, and even then had almost as many standing passengers as seated until Leeds. In order to let people board I had to put one sizeable item of luggage on my head so people could squeeze through the tiny gap.
Although the TPE experience was somehow even less comfortable than that on EMT (which I hadn't considered possible), it did last less time, as there was ample standing room by Leeds, so about 60 minutes. On that basis I'm not really sure which I think is the preferred option. Journey time wise they seem fairly similar, but the frequency of the Virgin and TPE services is higher, so that seems like it might be the better choice.