The rack you have chosen has to be the most bizarre rack I have ever seen. Trans-X generally make cheap and nasty stuff for
Halfords. I once bought a Trans-X suspension seat post. It was cheap and nasty. I doubt whether it will be very strong or light looking at the design.
The sort of rack you want is something like this Tortec Expedition which is a Cycling Plus Best Buy and won't break the bank at £30 from
Wiggle. It will certainly carry a lot more weight than the Trans X rack you are looking at and be many many times stronger and a lot more durable.
http://www.wiggle.co.uk/p/cycle/7/TorTec_Expedition_Alloy_Rear_Rack/5300003805/
Avoid Blackburn racks as they ARE crap. The welds are sh1t and break. I had welds break on two Blackburn EX-2 Expedition racks. The best racks are Tubus but if you look on the Wiggle site you will see they are pretty expensive. Typically cyclists who ride off around the world choose to fit them as they are steel meaning if they do break they can be welded up at some old guys shed in the back of beyond with the whole family and the goat looking on.
The panniers you have chosen look a bit weird as well. Nothing in their description mentions whether they are water resistant let alone waterproof. That bag affair on top I would avoid as it looks as if you can't detach it. It is best to carry weight lower down to keep centre of gravity low meaning the bike is not so top heavy and difficult to manoeuvre and control. By all means put stuff on the rack between and over the panniers but generally do it with a separate bag such as a dry bag such as Ortlieb do.
If fudget is a consideration which I suspect it is then go for something like the
Altura Arrans 46/36 litres which are well made and water resistant for light rain. If the rain starts to come down big time then Altura provide rain proof covers which although a bit of a pain to fit on and take off (it is not hard to do but can be a chore) but in reality you don't have to use them that often so it is only a minor gripe as they are excellent value. Plus the covers are bright yellow. They are the same design as the older version Orkneys which are the top make of Altura panniers. My black Orkneys have lasted 14 years and are still in excellent condition, although I now have a set of 100% waterproof Vaude Aqua panniers as well.
http://www.dalescycles.com/pannier_bags_s/107.htm
The Arran 36 litres don't have the side pocket. They are just one bag AFAIK which is a PITA as side pockets are essential IMHO. Altura stuff is reasonably priced and well made so you will get good use out of their gear.
If you have a decent wedge to spend on panniers then go for the Vaude Aqua range, Ortlieb Roller Classics or Altura Orkneys in this order. They are all good just that the Vaude Aqua panniers are the best.
HTH.
