There seems to be this misconception that the salary cap is £1.65m and totally inflexible, but in actual fact if you study the salary cap rules then its perfectly possible (and legal) for some clubs to already be paying at least £500k more than that to players.
On top of the basic £1.65m (which doesn't include National Insurance either) there are several other ways that clubs can pay the players...
1. Appearance Bonuses - if clubs pay their players appearance money on top of their contract money then only 18 games count towards the cap, therefore clubs can pay appearance money for the other 9 SL games and other salary cap relevant games (e.g. Challenge Cup, Play Offs etc) outside of the cap
2. Win Bonuses - as above but only 14 winning games count towards the cap, anything in excess of that is excluded
3. Prize Money - if a club pays a share of prize money from SL, Challenge Cup, World Club Challenge to its players then that is exempt from the cap
4. Challenge Cup - only QF, SF and Final are counted as salary cap relevant games so effectively the clubs can pay what they like to players in rounds 4 and 5.
5. Long service - there is a £50k dispensation for any club with players with more than 10 years service
6. Internationals - each club is allowed to deduct an amount from the salary cap spend each time a player they developed in their academy is picked to represent their country, up to a maximum of £100k per season. The player doesn't even have to be at their club anymore - e.g. if Westerman was picked for England then Cas would get the exemption and not Hull.
So its not as black and white as some seem to think. There are some top clubs who could quite easily be paying 30-40% over the "cap" as it stands.
You forgot to mention that London and Catalan automatically get the full International weighting.