How long should one stay with RRSP investments?
Sam & Sally are in the same tax bracket: T (T=.45 means a 45% tax bracket).
Sam invests $A INside and Sally invests $A OUTside an RRSP.
Sam also invests his tax refund of TA (T = income tax rate, right?) so his total investment is A(1+T).
After umpteen years, Sam's portfolio grows by a factor Y.
It's now AY and he cashes it in, pays the tax, and gets
A(1+T)Y (1-T) = A(1-T2)Y (after taxes).

Sally's portfolio grows by a factor X, so it's worth AX and she pays taxes on the Capital Gains of A(X-1), namely (3/4)T A(X-1) ... remember that her Capital Gains are taxed at 75% of her tax rate ... giving her
AX - (3/4)T A(X-1) = AX(1-(3/4)T) + (3/4)TA (after taxes).

In order for Sam to get more money (after taxes) than Sally, we gotta have:
A(1-T2)Y > AX(1-(3/4)T) + (3/4)TA
or
Y > { X(1-(3/4)T) + (3/4)T }/(1-T2)

Remember, X is Sally's gain and Y is Sam's.
The graph of Y vs X is:


Conclusion? When the gains are small, Sam needs a greater return than Sally in order to end up with more after-tax money!

Let's consider a simple case where each is in a 50% tax bracket and each has $8K to invest. Things look like this:
Gain = 2 (for both Sam & Sally):
Available Cash
Tax Refund
Initial Portfolio
Final Portfolio
Taxable Income
After-tax Income
Sam
8,000
4,000
12,000
24,000
24,000
24,000(1-(1/2))=12,000
Sally
8,000
0
8,000
16,000
8,000
16,000-(3/4)(1/2)8,000=13,000
See?
Sally wins!

Gain = 4 (for both Sam & Sally):
Available Cash
Tax Refund
Initial Portfolio
Final Portfolio
Taxable Income
After-tax Income
Sam
8,000
4,000
12,000
48,000
48,000
24,000
Sally
8,000
0
8,000
32,000
24,000
32,000-(3/4)(1/2)24,000=23,000
See?
Sam wins!

Of course, it ain't wise to cash in your portfolio all-at-once, so let's consider another scenario ( knowing that when the gain isn't too large, then investing OUTside an RRSP might be a better strategy):
We invest for 25 years, first by investing INside an RRSP then, after umpteen years, we switch to investing OUTside our RRSP (for the balance of the 25 years). At the end of 25 years we give ourselves a 20-year annuity with each of the INside and OUTside portfolios. We also assume that the annual return is 8% for both portfolios.
Here's a picture of our after-tax annual incomes from each of the INside and OUTside portfolios (and the TOTAL income) and how it depends upon the number of years (out of 25) that we invest INside (before we switch):


The interesting thing is that the strategy which provides the MAXIMUM income is neither always-INside nor always-OUTside!

The spreadsheet allows you to generate this graph using numbers of your own choosing.

P.S.
I am NOT suggesting a strategy here ... only that you shouldn't assume (without some cerebral gyration) that RRSPs are the only game in town!