Well it depends on what you mean by 'highest paid'?
If you look at basic salary then I think someone like MYT would be highest for charters, but then they have one of lowest hourly pay. If you look at flight pay then yes it's probably TOM or MON or someone.
For new crew the basic is just over 10k + usually a small inflation rise in April time. This then increases every year (for 3 years) you rejoin or are made permanent. So after 4 years you will be at the top of the crew payscale, without being promoted. The increase is usually about £800, so looking at about 13k basic after 4 years.
Flight allowance is £2.78 hour which is from check in time to ten mins after chocks I think. The only difference and money earner is when you are nightstopping away from base, when you are paid from check in until you return to your base, so paid for sleeping in hotel etc!
Providing you are trained on the 767 you can fly longhaul after 3 months with the company I think. Carmen rostering now also means that you can 'bid' for certain flights etc, so you can ask to be rostered longhaul trips, whether you get them or not depends! If you are at one of the biggest bases LGW or MAN you should get a fair share of trips though.
As for discounts I think all new crew are on the new concession scheme, but I doubt this will apply until you are permanent. The new scheme means you can take 6 return flights anywhere with TOM for a nominal price and you get a confirmed seat or not up to 48 hours before. Holiday wise you get a sum of money off TOM holidays which increases every year up to 3 years I think. So depending on the cost of the holiday it would more than likely be more than 10% off.
Hope that all helps if you can understand it, oh and there's some great crew!