Smallint Vs Int Join With Stats - Suprizing!

Is an index based on a smallint (16 bit) really faster than an index based on an int (32 bit)
If so, how much...

Four tables

Table A: ID smallint (PK)
Text varchar(50)

Table B:ForeginID smallint (indexed - non unique)
Text varchar(50)
rowID int (PK)

Table C: ID int (PK)
Text varchar(50)

Table D:ForeginID int (indexed - non unique)
Text varchar(50)
rowID int (PK)


Table A and C contain identical data
Table B and D contain identical data
(Tables A and B were filled and then copied to Tables C and D)

Tables A/C are loaded with 64,000 records (-32,000 to 32,000)
Tables B/D are loaded with 6,400,000 records ForeginID loaded randomly with values between -32,000 and 32,000


The purpose of this test is to find out if identical queries joined on a smallint are actually faster than int based.

I ran 3 queries on each set:
- Full select
- Select on ID/Foregin ID
- Select on Table2 RowID joined to table 1


Here are the queries:

#1. Full select (smallint) - grouped to limit result set
-----------------------------------------------------------
SELECT intAID, COUNT(intBID)
FROM TESTintA
INNER JOIN TESTintB ON intAID = intBID
GROUP BY intAID
ORDER BY COUNT(intBID) desc

#2. Select on ID/Foregin ID (smallint)
------------------------------------------
SELECT intAID, intBID, strATXT, strBTXT
FROM TESTintA
INNER JOIN TESTintB ON intAID = intBID
WHERE intAID = 29120


#3. Select on Table2 RowID joined to table 1 (smallint)
------------------------------------------
SELECT intAID, intBID, strATXT, strBTXT
FROM TESTintA
INNER JOIN TESTintB ON intAID = intBID
WHERE intPK = 1050


#4. Full select (int) - grouped to limit result set
------------------------------------------
SELECT lngCID, COUNT(lngDID)
FROM TESTlngC
INNER JOIN TEXTlngD ON lngCID = lngDID
GROUP BY lngCID
ORDER BY COUNT(lngDID) desc


#5. Select on ID/Foregin ID (int)
------------------------------------------
SELECT lngCID, lngDID, strTXTC, strTXTD
FROM TESTlngC
INNER JOIN TEXTlngD ON lngCID = lngDID
WHERE lngCID = 29120

#6. Select on Table2 RowID joined to table 1 (int)
------------------------------------------
SELECT lngCID, lngDID, strTXTC, strTXTD
FROM TESTlngC
INNER JOIN TEXTlngD
ON lngCID = lngDID
WHERE intPK = 1050



Here are the results: (run multiple times to verify)

#1. Full select (smallint) - grouped to limit result set
-----------------------------------------------------------
(8 seconds) - before computing statistics on table
(13 seconds) - after computing statistics on table


#2. Select on ID/Foregin ID (smallint)
------------------------------------------
(0 seconds)


#3. Select on Table2 RowID joined to table 1 (smallint)
------------------------------------------
(0 seconds)


#4. Full select (int) - grouped to limit result set
------------------------------------------
(8 seconds) - before computing statistics on table
(7 seconds) - after computing statistics on table

#5. Select on ID/Foregin ID (int)
------------------------------------------
(0 seconds)


#6. Select on Table2 RowID joined to table 1 (int)
------------------------------------------
(0 seconds)


Conclusion: Not only is there a negligible difference in select performance, generating stats on the smallint actually makes it slower.
(perhaps there is some kind of conversion going on here behind the scenes?)