Growth sounds very optimistic to me, check the data, for this specific age cohort, as while the 6.2-% return maybe correct overall, its less likely this is true for an older age group, whose risk profile is likely to be a little more conservative.
Recalculation needed on the Tax Relief, you are mixing up :
Age related Pension Limits
With
Actual Tax relief on Pensions
These are two totally different numbers.
So, for example 2012, joint income is 75k, so
Max age related Pension for PAYE relief is 30% of that = 22,500.(based on aged 50) This is the maximum amount, you can get tax relief for Pension based on current age, but this does not necessarily mean, you will receive relief at the higher 40 % tax rate.
Next, is the maximum possible tax relief, which is 22,500 @ 40 % = 9,000, and that only applies, if this amount of income was actually taxable at the 40 % rate, which seems very unlikely, if the total joint income is just 75k.
Tax bands are very impactful here, in 2012 the tax band for 2 was circa 65,600, meaning more than half of the tax relief, would be at the lower 20 % rate.
Conversely, pension relief can be brought forward to future years, if pension tax relief is not fully untilsed in year of payment.