your calculation seems to be simplified. According to the formula given in RFC 5452, the number of fake packets 'F' that are candidates to be accepted is given by :
P_s = D * R * W / ( N * P * I )
where I is the number distinct IDs available (which is 65536 in your case), P is the number of ports used, N is the number of authoritative nameservers for a domain, R is the number of packets sent per second by the attacker, W is the window of opportunity, in seconds and D is the average number of identical outstanding queries of a resolver (typically 1, see Section 5).
If D = 1 (typical value according to the RFC), W = 0.1 (typical value according to the RFC), N = 2.5 (average value according to the RFC), P = 1 (assume only one port is used) and I = 65536 (provided in your question). Then P_s can be simplified into :
P_s = R / 1638400
Thus, plugging in the necessary values, for P_s to be 0.99, R should be greater than 1622016 packets/s. Since we used W = 0.1 and you send 1024 false replies per request, then you need about 1622016 * 0.1 / 1024 = 15.84 attempts.
(Hope my calculation is correct)