Would you be willing to change case?
A 290 and a i5 should have about 360mm worth of radiator but if its silence your after, the more the better. If you don't mind going external, a single 1080 phobya radiator will be more radiator than you will need if you went tri fire 290's and is the most silent option as 4 180mm low speed silence fans could be used on the radiator instead of 9 x 120 fans. If you are worried about transporting it, use quick disconnects to make the radiator easily detachable.
The way i see it, a 1080 radiator will likely cost almost the same as a new case which sports good watercooling options. It will also mean that you will never be required to dish out more cash for more radiator if you wanted to add to the loop.
Watercooling isn't cheap though, how much do you have to spend for a gpu + cpu loop?
This would be my kit of choice for silence and performance with enough radiators and fan that adding two more 290's wouldn't be an issue. If you have some 180 fans spare, you can save yourself up to 80 quid. The ones i have specced are the best in the business for watercooling but are overkill until you add more GPU's. You could do this £90 cheaper by choosing a smaller radiator but itl be a fair bit noisier and will give you very little overclocking room. To cool both your CPU and GPU and any other parts you might add requires the loop to go external or to get a case to fit your current loop in, which might be the right route to go if you plan on expanding, since your current motherboard cant Crossfire.
YOUR BASKET
1 x
Watercool Radiator MO-RA3 9x120 PRO - black £159.95
1 x
EK Water Blocks EK-DCP 4.0 X-RES (Incl. Pump) £79.99
1 x
EK Water Blocks EK-FC R9-290X - Acetal £79.99
1 x
EK Water Blocks EK-Supremacy Clean CSQ - Nickel £52.99
4 x
Silverstone 180mm Fan SST-FM181 £22.99 (£91.96)
2 x
Primochill Primoflex Advanced Tubing 13/10 - Clear £5.99 (£11.98)
8 x
EK Water Blocks EK-CSQ Fitting 10/13mm G1/4 - Black £2.99 (£23.92)
Total : £500.77 (includes shipping : FREE).
This next build would allow you to move to a bigger motherboard and keep the loop internal. Will be noisier and will cost more down the line when you expand but money has been saved by getting a case to suit the expansion of watercooling and any extra cards you might add. Unfortunately doesnt include fans and adding more than a gpu and CPU will require more than a 360mm radiator (a 240 can be put on the roof).
YOUR BASKET
1 x
Corsair Carbide 540 High Airflow ATX Cube Case - Black (CC-9011030-WW) £129.95
1 x
EK Water Blocks EK-DCP 4.0 X-RES (Incl. Pump) £79.99
1 x
EK Water Blocks EK-FC R9-290X - Acetal £79.99
1 x
EK Water Blocks EK-Supremacy Clean CSQ - Nickel £52.99
1 x
EK Water Blocks EK-CoolStream PE 360 (Triple) £49.99
2 x
Primochill Primoflex Advanced Tubing 13/10 - Clear £5.99 (£11.98)
8 x
EK Water Blocks EK-CSQ Fitting 10/13mm G1/4 - Black £2.99 (£23.92)
Total : £428.80 (includes shipping : FREE).
End of the day cost between them wont be any different, main differences are as follows:
First build:
Case is the same
Loop is external
Radiator overhead is huge and so silence is easily achievable
Second build:
Case is changed allowing for motherboard upgrade and Crossfire
Loop is internal
Not as much radiator overhead and will be louder and probably not silent when overclocked (adding a 240mm radiator will make it silent until you add more blocks)