I agree with Def that paper statements shouldn't be an important consideration for your decision.
However, I think there are several question you should consider which he didn't mention. These are:
1) What kind of government bonds are these?
2) How big is your "large" portfolio?
3) Do you plan to actively trade them or borrow against them?
The reasons these are relevant are:
1) Type of bonds:
If they are inflation indexed bonds (TIPs) or other treasury cusips that IB doesn't trade, you may have a problem.
IB doesn't offer trading in all government bonds. For example, I wish IB would allow its customers to trade the treasury inflation indexed bonds which trade and settle just like all other government bonds. However, they have chosen not to do so. According to IB customer service (admittedly not the most reliable source) you cannot transfer a government bond to your account if IB doesn't trade it.
Perhaps Def has some insight on why IB has decided not to offer trading on some treasuries?
2. Portfolio size:
If your government holdings will push your IB account over the SIPC $500 thousand limit, then I think it would be a big mistake to make the transfer unless you intend to trade or margin the bonds with IB rather than just custody them. A passive treasury portfolio is very simple to custody at a variety of brokers since there are so few coupon payment dates, no corporate events, etc. Why not take advantage of the free $500k per account SIPC insurance by simply spreading them over the requisite number of brokers. I believe you can even custody them directly with Treasury by transferring them to your Treasury Direct account.
3. Trading/borrowing:
If you are considering trading or borrowing against the portfolio, then obviously you want them at a broker which has good capabilities in that respect. I know IB has excellent margin rates. (That's why I wanted to move some inflation indexed bonds there.) I can't comment on their current treasury bond trading features since they don't trade the bonds in which I am interested. However, I do know their initial attempt at trading corporate bonds was very poor.