Hi benwar and welcome to the forum
No-one can really advise you whether it is better for you to go bankrupt now, or tell you how the Official Receiver is likely to review your income and expenditure.
Reading between the lines with regard to your post, it seems that you are aggrieved at having to share your payrise with yorur creditors? If this is the case, then an IVA is probably not the right solution for you, and you will probably grow to resent it in the long-term.
The payments in bankruptcy last for 3 years because that is what the law states.
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
To have me propose an IVA for you, please visit:
http://www.melaniegiles.com/ivaEnquiry.asp
See customer feedback at:
http://www.iva.com/iva_companies/IVA_Advice_Bureau.asp