Hi Charles. There is a useful guide here:
http://pjgrecovery.com/clean-up-credit-rating.asp
The IVA and associated defaults ( if dated correctly) will disappear completely from the CRA files. Check for any Notice of Correction and ask for that to be removed too, as this has to be done manually.
Some lenders do, it seems, keep historic archives, especially those in the same group of companies of any of your old creditors, so an IVA could come to light. However, if you have responded honestly to any relevant questions, this should pose no problem.
Yes, an excellent credit rating is achievable, given time and good entries from well run accounts ( mobile phone, credit card, bank account etc).
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014